One way of making such an electrode is to take a metal support such as a perforated metal sheet and to coat or calender layers of active paste on its faces. The paste contains the active material together with a polymer which acts as a plastic binder, and its concentration is optimized with respect to three criteria:
the mechanical strength of the electrode which increases with increasing concentration of binder;
the electrical conductivity of the plastified mass which decreases with increasing binder concentration; and
its suitability for electrochemical operation which is a more complex criterion that takes into account several of the properties of the plastified mass: wettability by the electrolyte; and chemical compatibility and stability of the binder with the active material of the electrolyte; this suitability for electrochemical operation also decreases with increasing concentration of binder.
Electrodes are thus made whose mechanical strength is adequate for enabling storage batteries to be assembled and for ensuring adequate stability in electrode performance.
The manufacturing method includes a cutting stage in which the support coated with the active mass is cut out to a desired size. It has been observed that an electrode obtained in this way is mechanically weak along the lines of cut and that during subsequent manipulations inherent to assembly, the edges of the electrode crumble. Later on, during normal operation of the storage battery, losses of active matter are also observed around the edges and these may give rise to short circuits and consequenty to the storage battery being put out of service.
The present invention seeks to avoid this drawback.